Communication apparatus having function to record communication history

The present invention relates to a communication apparatus for detecting a fault which occurred in a communication system and for preventing the fault from propagating over the system.

According to the variation of needs of computer systems in various fields and advancement of the technologies, the systems tend to get enlarged and complicated. Thus, the needs of distributed systems which process jobs through a plurality of communication apparatus are becoming strong. In a distributed processing system, a plurality of communication apparatus are connected by means of communication paths. Thus, if a fault which results in losing a message occurs due to a trouble of a communication apparatus, data which was processed according to erroneous information is propagated to other communication apparatus and thereby erroneous data is output as the entire system output. To prevent that, it is necessary to always monitor processes of each communication apparatus. If a trouble or an error is detected, it is necessary to stop the operation of the communication apparatus in which the trouble or the error occurred so as to prevent a bad effect which results from the trouble or the error from propagating to other communication apparatus.

To solve such a problem, thus far, for example, communication apparatus are multiplexed and received messages are compared to detect troubles and errors of the communication apparatus.

However, in such a method, the control of multiplexed communication apparatus becomes complicated and it is necessary to wait until a plurality of messages are received, thereby decreasing the process speed of the entire system.

The inventors of the present invention and the concerned persons proposed "Trouble and/or error detection method of communication subjects by adding communication cumulative amount to transmission messages and by comparing communication cumulative amount of reception messages with communication cumulative amount intrinsic to the communication subject" (Japanese Patent Application Sr. No. 63-297777).

In the aforementioned method, the disadvantage of the multiplex system is cleared and the overhead of process execution is reduced, in the communication system such as CSMA/CD system where data is retransmitted when a collision is detected. However, if transmission requests of Message A and Message B occur at the same time in different communication apparatus, although Message A is transmitted after Message B is received, Message A with communication cumulative amount, which does not account the arrival of Message B, is transmitted. Thus, even if data is correctly communicated, an inconsistency of communication cumulative amount takes place and the receiving communication apparatus supposes that a trouble occurred in the transmitting communication apparatus.

Thus, as a communication apparatus which allows an overhead of execution processes and halt time due to a trouble to be as small as possible, it is necessary to remove the inconsistency of communication cumulative amount even if a message is retransmitted due to an occurrence of collision.

An object of the present invention is to solve the aforementioned problems, namely, to reduce the overhead of processes of a communication apparatus so as to use it in a real time control and the like and to prevent a bad effect due to a trouble or an error of a communication apparatus from propagating to other ones.

The communication apparatus of the present invention has means for storing communication cumulative values each representing the amount of messages transmitted by a message transmitting means associated with communication apparatus and each of said plurality of the other communication apparatus. When the communication apparatus receives a message transmitted by other communication apparatus, the communication apparatus compares cumulative values included in the message to cumulative values stored in the storing means. If the comparison is negative, the communication apparatus executes an error process. So, it is possible to reduce the overhead of processes of a communication apparatus so as to use it in a real time control and the like and to prevent a bad effect due to a trouble or an error of a communication apparatus from propagating to other ones.

FIG. 1 is a structural diagram showing the structure of an embodiment of the present invention;

FIG. 2 is a structural diagram showing the structure of a communication process section of FIG. 1;

FIG. 3 is a structural diagram showing the structure of a communication cumulative table of the embodiment of the present invention;

FIG. 4 is a diagram showing an example of a message of the embodiment of the present invention;

FIG. 5 is a flow chart showing a transmission process operation; and

FIG. 6 is a flow chart showing a reception process operation.

By referring to the accompanying drawings, an embodiment of the present invention will be described in the following.

FIG. 1 is a structural diagram showing the structure of a communication apparatus of an embodiment of the present invention.

As shown in the figure, the communication apparatus comprises a communication path 1 and a plurality of communication apparatus 2a, 2b, . . . (hereinafter named the communication apparatus 2 as a general term) which are connected to the former. Each communication apparatus 2 comprises main process section 3a, 3b . . . (hereinafter named the main process section 3 as a general term) and communication process section 4a, 4b, . . . (hereinafter named the communication process section 4 as a general term) for executing information exchange between the communication apparatus 2 connected to the communication path 1. In other words, the communication apparatus 2 sends a message to the communication path 1 and receives a message from the communication path 1 so as to execute the information exchange with another communication apparatus 2 through the communication process section 4.

FIG. 2 shows the structure of the communication process section 4.

As shown in the figure, the communication process section 4 comprises a transmission process section 5, a reception process section 6 and a comparison process section 7. The transmission process section 5 is associated with the comparison process section 7 so as to execute a transmission process of a message which is transferred from the main process section 3. On the other hand, the reception process section 6 is associated with the comparison process section 7 so as to execute a reception process of a message from the communication path 1.

As shown in FIG. 3, the comparison process section 7 stores the number of messages which are passed through the communication path 1 as a communication cumulative amount table in order to represent the communication history thus far. The communication cumulative amount is composed of an individual communication cumulative amount section 8 where each communication apparatus 2 stores the communication cumulative amount for each of other communication apparatus which are senders of receipt messages and a total communication cumulative amount section 9 which represents the communication cumulative amount of the entire system, namely, the total value of the individual communication cumulative amount section 8. The number of columns that the individual communication cumulative amount section 8 requires is the number of the communication apparatus 2 connected to the communication path 1. In the example shown in FIG. 3, eight communication apparatus 2 designated a to h are connected. When a message is received or transmitted, one line of the communication record is newly added to the communication cumulative amount table and the communication cumulative amount table is updated. Thus, the line of the maximum value of the total communication cumulative amount section 9 represents the latest communication cumulative amount.

In the embodiment, the communication cumulative amount is defined as the number of transmissions.

Now, by referring to an example of message format shown in FIG. 4, a transmission flow chart shown in FIG. 5, and a reception flow chart shown in FIG. 6, operations of the embodiment of the present invention will be described in the following.

First of all, a transmission process which transmits a message from the main process section 3 to the communication path 1 will be described.

The transmission process section 5 receives a message which is transferred from the main process section 3 through a route 10. The transmission process section 5 also executes the following process in association with the comparison process section 7. Namely, the transmission process section 5 requests the comparison process section 7 to transfer a tab with the latest communication cumulative amount from the communication cumulative amount table through a route 11 (in step S1). When the comparison process section 7 receives this request, it picks up the tap representing the latest communication cumulative amount and sends it to the transmission process section 5 through a route 12 (in step S2). The transmission process section 5 adds the latest communication cumulative amount transferred from the comparison process section 7 to a message transferred from the main process section 3 (in step S3). In other words, as shown in FIG. 4, the transmission process section 5 generates a message in such a format that a destination ID, a sender ID of the transmission process section 5 in the communication apparatus 2 and the communication cumulative amount which has been received are added to a message main text, and broadcasts the message to the communication path 1 through a route 13 (in step S4).

After the transmission process section 5 normally completed the transmission of the message, it notifies the comparison process section 7 of the completion of the message transmission (in step S5). When the comparison process section 7 received the notification of the completion of the message transmission, it newly adds one tab whose individual communication cumulative amount sections 8 corresponding to itself and the total communication cumulative amount section 9 are greater than those of the latest communication cumulative amount just by 1, so as to record the state of the completion of transmission on the communication cumulative amount table (in step S6).

Now, a reception process where the communication apparatus 2 receives a message from the communication path 1 will be described in the following.

A message from the communication path 1 is received by the reception process section 6 through a route 14 (in step S11). When the reception process section 6 received the message from the communication path 1, it transfers the received message to the comparison process section 7 through a route 15 so as to check whether or not the received message is correct.

When the comparison process section 7 received the message through the route 15, it searches the tab in the communication cumulative amount table which has the same communication cumulative amount as that of the received message (in step S12). If both communication apparatus which send and receive that message behave correctly, obviously the tab which has the same communication cumulative amount as that of the received message exists in the communication cumulative amount table of the message receiving communication apparatus. At that time since the communication cumulative amount is the number of communications, it is obvious that the tab which should be found exists just n tabs apart from the latest comulative amount, where n is the difference between the total communication cumulative amount section 9 of the latest communication cumulative amount and that of the received message. Thus, the tab to be compared can be immediately found. Comparison of communication cumulative amount is performed as follows.

As the first step, a comparison of values in the total communication cumulative amount sections 9 is made (in step S13). If they do not match, it is assumed that a communication error takes place in the communication apparatus 2 of the corresponding message sender, and an error process is executed (in step S14). Thus, the message main text is not transferred to the main process section 3. Instead, a trouble notification of the communication apparatus 2 is transferred to the communication path 1 through the route 12. When the reception process section 6 receives the trouble notification from the predetermined number of communication apparatus within the predetermined period of time, the reception process section 6 determines that the trouble occurred in the communication apparatus 2 and then stops its operation. Moreover, if necessary, the reception process section 6 notifies the trouble of the communication apparatus 2 to the main process section 3 through routes 16 and 17.

On the other hand, when values in the total communication cumulative amount sections 9 are matched, the individual communication cumulative amount sections 8 are compared (in step S15). When they do not match, an error process similar to the aforementioned one is executed (in step S14). When the value of the total communication cumulative amount section 9 and that of the individual communication cumulative amount section 8 are matched, it is assumed that a correct message has been received and the state of reception completion is newly recorded on the communication cumulative amount table. Accordingly a tab, whose values of the individual communication cumulative amount section 8 corresponding to the message sender and the total communication cumulative amount section 9 are greater than those of the latest communication cumulative amount by just one is added to the communication cumulative amount table (in step S16). In addition, it is determined whether or not the destination of the message is the communication apparatus 2 to which the comparison process section 7 belongs (in step S17). When the destination is the communication apparatus 2 to which the comparison process section 7 belongs, the notification of the normal reception is made through the route 16 and the message main text is transferred from the reception process section 6 to the main process section 3 through the route 17 (in step S18). When the destination is not the communication apparatus 2 to which the comparison process section 7 belongs, the message main text is not transferred to the main process section 3.

Now, the case that a communication request is issued from both the communication apparatus 2a and 2b at the nearly same time will be described in the following. As shown in FIG. 3, assuming that the latest communication cumulative amount in the communication cumulative amount table has values "3" and "10001001" as the total communication cumulative amount section 9 and the individual communication cumulative amount section 8 respectively, and the communication cumulative amount is added to the messages from the communication apparatus 2a and 2b and the resultant messages are broadcast to the communication path 1. It is assumed that the communication apparatus 2c will receive the message from the communication apparatus 2a, for example. When the communication apparatus 2c received the message from the communication apparatus 2a, it compares the communication cumulative amount table stored in the own comparison process section 7c with the received communication cumulative amount. Since there is a tab where values are matched both in the total communication cumulative amount section 9 and the individual communication cumulative amount section 8, a tab where the value of the total communication cumulative amount section 9 and the value of the individual communication cumulative amount section 8 are "4" and "20001001", respectively, is added, and the communication cumulative amount table is updated to record the state where the message has been completely received. The added communication cumulative amount becomes the latest communication cumulative amount.

After that, the message from the communication apparatus 2b is received by the communication apparatus 2c. Although the communication cumulative amount included in the message is not matched with the latest communication cumulative amount which has been added in the communication apparatus 2c, since the communication cumulative amount preceding the latest communication cumulative amount is stored as history data, it is assumed that the message is correct and the message is received by the communication apparatus 2c. Then the line whose total communication cumulative amount section 9 and the individual communication cumulative amount section 8 are "5" and "21001001", respectively is added.

As was described above, since the communication cumulative amount is divided into the total section and the individual section and they are stored in a table format as history data, even if transmission requests are issued from a plurality of sites at the same time, no inconsistency of the communication cumulative amount takes place. Thus, the communication cumulative amount inconsistency which results from simultaneous transmissions from the plurality of sites can be prevented. And, messages which are transmitted simultaneously from the plurality of sites can be received.

Thus, in accordance with the communication apparatus of the present invention, since the communication cumulative amount is stored in a table format as history data, a communication error caused by a communication subject which fails to read a message and the resultant faulty propagation can be prevented without multiplexing the communication apparatus. Moreover, since it is not necessary to multiplex the communication apparatus, complication due to multiplication of processes of individual communication apparatus can be prevented. Furthermore, decrease of process speed necessary for waiting until messages are received from all multiplexed communication apparatus can be prevented.

The present invention is not limited to the aforementioned embodiment.

For example, in the aforementioned embodiment, the number of transmissions was used for the communication cumulative amount. However, it is possible to use the message length, check sum value, and so forth.